1. Field of the Invention
This invention relates to an automatic sensitivity adjustment apparatus for use in the calibration of nondestructive inspection instruments such as ultrasonic, eddy-current and magnetic flaw detectors.
2. Description of the Prior Art
For the detection of flaws in materials such as steel rod, steel pipe or other products having a circular cross-section by means of a nondestructive inspection instruments of the above type, there is known a method in which a detecting sensor is caused to scan the surface of the work in a spiral path. For the detection of flaws in materials having a flat surface such as steel plate and billet, the sensor is driven traversely to scan the surface of the test piece in a zigzag manner. However, in order that such flaw detection may be sufficiently accurate, the nondestructive inspection instrument need be previously calibrated using a control reference standard similar to the test piece in dimensions and grade of material. This calibration has heretofore been accomplished manually by a visial monitoring of the amplitudes of pulse-waves displayed on a cathode-ray tube or a recorder, which is either built into the nondestructive inspection instrument or externally connected to the instrument. However, because in such a calibration procedure, the scanning of the sample piece by the sensor takes place under the same conditions as in actual testing, the aforesaid pulse-wave is obtainable only once per revolution in the case of spiral scanning and only twice per reciprocation in the case of zigzag scanning. This means that the signal display of the cathode-ray tube is unsatisfactory in the duration of the display and the display of the recorder is unsatisfactory in follow-up performance. Particularly where a plurality of sensors are employed, calibration is the time-consuming procedure and cannot necessarily be fully accurate.
This invention has been developed to overcome the above disadvantages and has as its object to provide an automatic sensitivity adjustment apparatus which holds the peak value of an intermittent pulse signal for a predetermined time and performs an automatic and accurate calibration of a nondestructive inspection instrument.